1. Field of the Invention
The present invention relates to a driving apparatus for a ceiling fan; more particularly, the present invention relates to a driving apparatus for the DC brushless motor of a ceiling fan, the driving apparatus of which comprises a coder and a sensor disposed outside the DC brushless motor.
2. Descriptions of the Related Art
DC brushless motors have several advantages, such as high torque at low speed, low electromagnetic interference, no noise, and maintenance free of carbon brushes. However, to maintain smooth operation of a DC brushless motor, and to have it start successfully from a stationary state, electromagnetic sensors (e.g., hall sensors) have to be placed in these motors to sense the variation of the magnetic field due to positional variation of the magnetic poles relative to the stator. The controller of the DC brushless motor can then supply power to stator coils in response to output of the sensors to ensure continuous and steady operation of the motor.
Inside the DC brushless motor is a rotor made of a permanent magnetic material. In order to determine the rotational position of the motor, hall sensors are arranged inside the motor corresponding to position of the stator, so that the positional variation of the magnetic poles resulting from rotation of the rotor can be sensed for the purpose of motor driving. Upon startup of the motor, the hall sensors consciously sense each rotation of the motor, so that the control circuit can drive the motor in a steady manner.
Taking a three-phase DC brushless motor for a ceiling fan as an example, the motor comprises three electromagnetic sensors. Since the electromagnetic sensors are located inside the motor, some destructive processes such as drilling are preformed on the hardware in order to route the transmission lines between the motor and the controlling circuit for transmitting output signals from the electromagnetic sensors. For example, the number of connection holes need to be opened on the motor axle, so that the transmission lines can pass through to connect with the controller. Obviously, such large connection holes may compromise the integrity of the motor axle, and put the user in danger after long periods of service.
Furthermore, conventional motors used in ceiling fans are manually controlled, which means that control operations such as rotation speed adjustment and turning-on/-off of the motors are performed in a contact mode. In the conventional operation mode, rotation speed of the motors can only be controlled in a round-robin switching manner, in which case, once the motors are turned off, they can only be restarted at the next speed but not at the previous speed. To obtain the same speed as that before it is turned off, the user has to turn on and off the motor in succession through the entire operation cycle, which is particularly inconvenient.
Further, when the fan operates under an increased load, if the controller is not provided with a protection function, the motor overheat or even fail under an unendurable load.
In view of this, it is highly desirable in the art to provide a driving apparatus that can start up and drive a DC brushless motor for a ceiling fan without the need of electromagnetic sensors, and a controller that can store a previous rotation speed of a DC brushless motor while being provided with a protection function.